A disk drive, such as a magnetic disk drive, comprises a magnetic disk, spindle motor, magnetic head, and carriage assembly. The magnetic disk is disposed in a case. The spindle motor supports and rotates the disk. The magnetic head reads data from and writes data to the disk. The carriage assembly supports the head for movement relative to the disk. A head section of the magnetic head comprises a recording head for writing and a reproduction head for reading.
Magnetic heads for perpendicular magnetic recording have recently been proposed in order to increase the recording density and capacity of a magnetic disk drive or reduce its size. In one such magnetic head, a recording head comprises a main pole configured to produce a perpendicular magnetic field, return or write/shield pole, and coil. The return pole is located on the trailing side of the main pole with a write gap therebetween and configured to close a magnetic path that leads to a magnetic disk. The coil serves to pass magnetic flux through the main pole.
To improve the recording density, a magnetic head based on high-frequency magnetic field assist recording is proposed in which a spin-torque oscillator for use as a high-frequency oscillation element is disposed between main and return poles. A high-frequency magnetic field is applied from the spin-torque oscillator to a magnetic recording layer. This magnetic head is configured so that the distance between the respective facing surfaces of the main and return poles is reduced to enlarge a gap magnetic field.
In the case of the magnetic head described above, however, the main and return poles are located near the spin-torque oscillator. Further, the main and return poles are each formed of a continuous magnetic film. Therefore, magnetization of the main and return poles fluctuates due to a high-frequency magnetic field produced as the spin-torque oscillator oscillates, whereupon spin waves occur in the main and return poles. An energy loss due to the spin waves increases, so that oscillation of the spin-torque oscillator is suppressed. Consequently, the intensity of a high-frequency magnetic field for the magnetization reversal of a recording layer of a perpendicular recording medium becomes insufficient, so that it is sometimes difficult to achieve sufficient recording capability.